Mounting structure for variable nozzle mechanism in variable-throat exhaust turbocharger

ABSTRACT

Provided is a variable-throat exhaust turbocharger in which a nozzle assembly including a nozzle mount and nozzle vanes has a firm support structure without affection by a thermal deformation of a turbine casing and an external force exerted to the turbine casing, and a scroll portion is formed in a substantially opened configuration so that the nozzle assembly can be simply formed in order to reduce the number of mold cores for a scroll during casting of the turbine casing, thereby it is possible to enhance the productivity of the turbine casing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mounting structure for a variablenozzle mechanism which is used in a variable-throat exhaustturbocharger, and which introduces exhaust gas from an engine (internalcombustion engine) to apply the exhaust gas onto a turbine rotor by wayof a scroll and a plurality of nozzle vanes formed in a turbine casing,and which is configured so as to change the blade angles of theplurality of nozzle vanes.

2. Description of the Related Art

A patent document 1 (Japanese Patent Laid-Open No. 2001-207858)discloses an example of a relatively small-sized turbocharger which isused for a vehicle internal combustion engine or the like, and in whichengine exhaust gas charged in a scroll within a turbine casing is fedthrough a plurality of nozzle vanes provided on the inner peripheralside of the scroll, and is then applied to a turbine rotor provided onthe inner peripheral side of the nozzle vanes. Further, there have beenprosperously used a variable-throat radial flow exhaust turbochargerincorporating a variable nozzle mechanism which is capable of changingthe blade angle of a plurality of nozzle vanes.

Further, as for example, Japanese Patent document 2 (Japanese PatentLaid-Open No. 2004-132367) discloses another example of thevariable-throat radial flow exhaust turbocharger incorporating avariable nozzle mechanism.

Referring to FIG. 12, which shows a conventional example of thevariable-throat radial flow exhaust turbocharger incorporating theabove-mentioned variable nozzle mechanism, in a sectional view along therotating axis thereof, there are shown a turbine casing 10, a scroll 11formed in a spiral-like configuration on the outer peripheral side ofthe turbine casing 11, and a radial flow turbine rotor 12 arrangedcoaxially with a compressor 8. The turbine rotor 12 has a turbine shaft12 a which is rotatably journalled to a bearing housing 13 through theintermediary of a bearing 16. Further, there are shown a compressorhousing 7 accommodated therein with the compressor 8, an air inlet 9 ofthe compressor housing, spiral air passages 7 a and the rotating axis100 a of the exhaust turbocharger.

Further, there are shown a plurality of nozzle vanes 2 which arearranged in the circumferential direction of the turbine on the innerperipheral side of the scroll 11 at equal intervals. Each of the nozzlevanes 2 is coupled at its end part with a nozzle shaft 02 which isrotatably supported in a nozzle mount 4 secured to the turbine casing10. Further, the blade angle of the nozzle vanes can be changed by avariable nozzle mechanism 100.

In the variable nozzle mechanism 100, the nozzle vanes 2 are arrangedbetween the nozzle mount 4 and an annular nozzle plate 6 which iscoupled to the nozzle mount 4 through the intermediary of a plurality ofnozzle supports. Further the nozzle plate 6 is fitted in an attachingpart of the turbine casing 10.

There is shown a drive ring 3 which is formed in a disc-like shape andwhich is rotatably supported to the turbine casing 10. The drive ring 3is fixed thereto with drive pins 32 at circumferentially equalintervals. There are shown lever plates 1 each having on the inlet sidea groove which is engaged therein with the associated drive pin 32, andfixed on the outlet side to the associated nozzle shaft 02.

There are shown a link 15 couple to a drive source (which is not shown)for the nozzle vanes 2, and a pin 14 which is coupled to the link 15.The pin 14 is engaged with the drive ring 13 which is therefore rotated.

During the operation of the variable-throat exhaust turbochargerincorporating the variable nozzle mechanism having the above-mentionedconfiguration, exhaust gas from an engine (which is not shown) is ledinto the scroll 11 so as to be swirled along spiral passages in thescroll, and is then introduced through the nozzle vanes 2. Then theexhaust gas flows through the gaps between the vanes and then flows ontothe turbine rotor 12 from the outer periphery of the latter. Thereafter,the exhaust gas flows radially toward the center of the turbine rotor 12so as to carry out an expansive work to the turbine rotor 12.Thereafter, the exhaust gas axially flows being led to a gas outlet 10 bfrom which the exhaust gas is discharged, outside of the supercharger.

In order to control the delivery volume of the above-mentionedvariable-throat turbine, an blade angle of the nozzle vanes 2 is set inthe actuator by an blade angle control means (which is not shown) inorder to regulate the flow rate of exhaust gas passing through thenozzle vanes to a desired value. The reciprocal displacement of theactuator in response to the thus set blade angle is transmitted by wayof the link 15 and the pin 14 to the drive ring 13 which is thereforerotated.

The rotation of the above-mentioned drive ring 3 causes drive pins 32which are secured to the drive ring 3 at equal intervals in thecircumferential direction thereof to rotate the lever plates 1 aroundthe nozzle shafts 02. Due to the rotation of the nozzle shafts 02, thenozzle vanes 2 are configured so as to be turned in order to change theblade angle thereof up to the value set to the actuator.

Further, Patent Document 2 (Japanese Patent Laid-Open No. 2004-132367)discloses another example of the variable-throat radial flow exhaustturbocharger, which incorporates the above-mentioned variable nozzlemechanism.

However, the conventional variable-throat radial flow exhaustturbocharger incorporating the above-mentioned variable nozzlemechanism, which is shown in FIG. 12 and which is disclosed in thePatent Document 1 (Japanese Patent Laid-Open No. 2001-207858), thePatent Document 2 (Japanese Laid-Open No. 2004-132367) or the like, hasraised the following problems which should be solved:

In the variable-throat radial flow exhaust turbocharger incorporatingthe variable nozzle mechanism 100, as shown in FIG. 12, a drive force istransmitted from an actuator having a diaphragm or a motor drivenactuator to the drive ring 3 by way of the link 15 and the pin 14. Thus,the drive ring 3 is rotated, and accordingly, the drive pins 32 rotatethe lever plates 1 around the nozzle shafts 02 through the rotation ofthe drive ring 3. Due to the rotation of the nozzle shafts 02, thenozzle vanes 2 are turned so as to change the blade angle thereof to avalue set by the actuator.

In the variable nozzle mechanism 100 having the configuration as statedabove, the above-mentioned nozzle plates 6 may serve as slide surfaceson which the above-mentioned nozzle vanes 2 slide, and accordingly, itis sufficient to allow the nozzle plates 6 alone to have an acidresistance and a strength which can prevent deformation. Thus, thedurability of the variable nozzle mechanism can be prevented from beingaffected by a strength or the like of the turbine casing 10.

Meanwhile, a nozzle assembly composed of the nozzle vanes 2, the nozzleplates 6, the nozzle supports 5, the nozzle mount 4 and the like is heldby the nozzle mount 4 whose outer peripheral flange is supported by theinner diameter side flange of the turbine casing 10.

Thus, the nozzle mount 4 which is a main support member for the nozzleassembly is supported by the turbine casing 10. Thus, should the turbinecasing 10 be thermally deformed, or should an large external force beexerted to the turbine casing 10, the turbine casing 10 would possiblybe largely deformed.

As a result, a fastening force with which the nozzle mount 4 issupported by the turbine casing 10 would be greatly decreased. Thus,there would be caused such a problem that the structure for securing themain body of the nozzle assembly including the nozzle mount 4 to theturbine casing 10 side is damaged during operation of the turbocharger.

Thus, the nozzle assembly is excited by vibration from the engine, andaccordingly, the nozzle assembly and the nozzle link mechanism coupledto the former are worn so as to lower the function of the variablenozzle mechanism 100. As a result, the boost pressure (air supplypressure) to the engine is greatly lowered.

Meanwhile, the variable displacement type exhaust turbochargerinevitably has a cut part 11 s which defines a scroll underline in thelower portion of the scroll 11 in the turbine casing 10. Accordingly, inorder to increase the sectional area A of the scroll 11, it is requiredto enlarge the scroll in both radial and axial directions for increasingthe sectional area A thereof. As a result, there would be caused such aproblem that the turbine casing 10 becomes large-sized.

In particular, in the case of enlarging the scroll 11 in the radialdirection of the turbine, the distance R between the rotating centeraxis 100 a and the center of the sectional area of the scroll 11 becomesalso larger, and accordingly, there would be caused such a problem thatthe ratio A/R between the sectional area A and the distance R is not soappreciably increased.

Meanwhile, if the distance R is decreased, it is necessary to shift thescroll 11, radially inward. In this case, there would be caused aconstraint since a turbine outlet diffuser or the like is arranged,radially inward, and accordingly, there would be caused such a problemthat the shifting of the scroll as stated above is difficult.

Further, the distance R to the center of the sectional area can bedecreased by flattening the scroll 11 in the radial direction of theturbine. However, there would be caused such a problem that the scroll11 itself becomes longer in the axial direction of the turbine.

Further, as stated above, since the ratio A/R between the sectional areaA and the distance R is set to be large, the scroll 11 shown in FIG. 12is formed therein with the undercut part 11 s in order to cause theturbine outlet side to have a large bulge. This undercut part 11 a isadvantageous in order to ensure a satisfactory aerodynamic performance.However, the manufacture of a mold core for the scroll of the turbinecasing 10 having the under cut part 11 s causes a high degree ofdifficulty in working, resulting in a problem of low productivity.

In this configuration, as stated above, a flange lit is present on theinner diameter side of the turbine casing 10. Thus, the turbine casing10 itself is not opened axially as viewed as a single element, andaccordingly, the number of mold cores for the scroll becomes larger. Asa result, there would be caused such a problem that the productivity ofthe turbine casing is hindered.

Further, the turbine casing is usually made of cast iron. However, theabove-mentioned structure inevitably requires split-type core, andaccordingly, there would be caused that burring is possibly causedwithin the scroll 11.

SUMMARY OF THE INVENTION

The present invention is devised in view of the above-mentioned problemsinherent to the prior art, and accordingly, an object of the presentinvention is to provided a nozzle assembly including a nozzle mount andnozzle vanes, which has a firm support structure while avoidingreceiving affection by a thermal deformation of a turbine casing or anexternal force applied to the turbine casing.

Another object of the present invention is to facilitate the formationof the nozzle assembly by simplifying a scroll portion so as to have asubstantially opened configuration.

Further, another object of the present invention is to provide avariable-throat exhaust turbocharger with enhanced productivity of aturbine casing by decreasing the number of mold cores for the scroll,used during casting of the turbine casing.

In order to achieve the above-mentioned objects, according to thepresent invention, there is provided such a configuration that exhaustgas from an engine is led through a scroll formed in a turbine casingand a plurality of nozzle vanes arranged on the inner peripheral side ofthe scroll, and is then adapted to act upon a turbine rotor provided onthe inner peripheral side of the nozzle vanes.

Further, according to the present invention, there is provided avariable-throat exhaust turbocharger incorporating a variable nozzlemechanism in which the plurality of nozzle vanes are rotatably supportedon an annular nozzle mount so as to change the blade angle of the nozzlevanes in order to regulate the volume of the exhaust gas fed onto theturbine rotor.

Further, according to the present invention, there is provided such aconfiguration that is characterized by an insert member which is formedin an annular shape, and which is removably mounted to the outerperiphery of the nozzle mount.

Further, according to the present invention, there is provided such aconfiguration that is characterized in that the outer periphery of theinsert member is fitted in an attaching bore which is formed so as to beopened from the scroll of the turbine casing toward the bearing housing,in order to mount the insert member to the bearing housing.

Further, the present invention specifically includes the followingconfigurations:

(1) The nozzle mount and the insert member are integrally incorporatedwith each other so as to constitute an integrated nozzle mount typeinsert member, and the integrated nozzle mount type insert member isfitted at its outer periphery in an attaching bore which is formed inthe turbine casing so as to be opened from the scroll toward the bearinghousing in order to attach the integrated nozzle mount type insertmember to the bearing housing;

(2) The insert member is attached thereto with a variable nozzlemechanism including the nozzle mount and nozzle vanes mounted to thenozzle mount so as to constitute an assembly structure of the nozzlemount and the insert member which are integrally incorporated with eachother. The assembly structure of the nozzle mount and the insert memberis secured to the bearing housing by means of fastening membersincluding bolts and attaching screws;

(3) The insert member is formed at its outer peripheral part with aflange which is then clamped between flanges formed in the turbinecasing and the bearing housing, and the thus obtained clamped parts arejoined at its outer periphery together in a fluid tight manner by meansof a coupling.

(4) A snap ring is fitted in a ring groove formed in the side end partof the bearing housing in the turbine casing. The outer peripheral partsof the bearing housing and the insert member are clamped between theinside of the snap ring and the turbine casing, that is, the bearinghousing and the insert member are fixed to the turbine casing by theinside surface of the snap ring.

(5) A female thread is formed in the attaching bore of the turbinecasing while a male thread is formed at the outer peripheral part of theinsert member. The female thread is engaged with the male thread so asto secure the outer peripheral part of the insert member between theturbine casing and the bearing housing.

(6) The outer peripheral part of the insert member is welded to thebearing housing and the turbine casing;

(7) A piston ring for fluid tight sealing is inserted between the outerperiphery of the insert member and the inner periphery of the attachingbore of the turbine casing so as to make the outer peripheral surface ofthe piston ring into slidable contact with the inner peripheral surfaceof the attaching bore in the turbine casing.

(8) A piston ring for fluid tight sealing is inserted between the innerperipheral surface of the insert member and the outer peripheral surfaceof nozzle mount which is opposed to the above-mentioned inner peripheralsurface.

Further, according to the present invention, there is provided avariable-throat exhaust turbocharger incorporating a variable nozzlemechanism, characterized in that an opening which has no protrusionprojected from the inner peripheral surface of the scroll in the turbinecasing toward the outer peripheral side thereof, and which is axiallylinear is formed in the turbine casing. Further, the present inventionis characterized in that an insert shroud having a protrusion projectedtoward the outer peripheral side and serving as a part of the innersurface of the scroll is attached to the opening, and the support partof an annular nozzle plate which is coupled to the nozzle mount throughthe intermediary of the nozzle supports is formed in the insert shroud.

Further, according to the present invention, there is provided avariable-throat exhaust turbocharger incorporating the variable nozzlemechanism, characterized in that an insert member formed in an annularshape is removably attached to the outer periphery of the nozzle mount,and the outer periphery of the insert member is fitted in an attachingbore which is formed so as to be opened from the scroll of the turbinecasing toward the bearing housing side in order to mount the insertmember to the bearing housing. Further, the present invention ischaracterized in that an opening having no protrusion which is projectedfrom the inner peripheral part of the scroll of the turbine casingtoward the outer peripheral side thereof and which is axially linear isformed in the turbine casing, then an insert shroud having a protrusionprojected toward the outer peripheral part of the scroll, and whichserves as a part of the inner surface of the scroll is attached to theopening, and a support part of an annular nozzle plate which is coupledto the nozzle mount through the intermediary of the nozzle supports isformed in the insert shroud.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a relevant part on theturbine side of a variable-throat exhaust turbocharger equipped with avariable nozzle mechanism of a first embodiment of the presentinvention.

FIG. 2 is an enlarged view illustrating a Z part in FIG. 1 of the firstembodiment.

FIG. 3 is a longitudinal sectional view of a relevant part in an upperhalf on the turbine side of a second embodiment of the presentinvention.

FIG. 4 is a view illustrating a third embodiment of the presentinvention, corresponding to FIG. 2.

FIG. 5 is a view illustrating a fourth embodiment of the presentinvention, corresponding to FIG. 2.

FIG. 6 is a view illustrating a fifth embodiment of the presentinvention, corresponding to FIG. 2.

FIG. 7 is a view illustrating a sixth embodiment of the presentinvention, corresponding to FIG. 2.

FIG. 8 is a view illustrating a seventh embodiment of the presentinvention, corresponding to FIG. 2.

FIG. 9 is a view illustrating an eighth embodiment of the presentinvention, corresponding to FIG. 2.

FIG. 10A is a sectional view of a relevant part of a turbine casing partin a ninth embodiment of the present invention.

FIG. 10B is a side view illustrating a turbine casing in the ninthembodiment.

FIG. 11 is a view illustrating a tenth embodiment of the presentinvention, corresponding to FIG. 1.

FIG. 12 is a longitudinal sectional view illustrating a variable-throatexhaust turbocharger equipped with a conventional variable nozzlemechanism.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Explanation will be hereinbelow made the present invention in the formof preferred embodiments of the present invention which are shown in theaccompanying drawings. It is noted here that the dimensions, thematerials, the shapes, and the relative arrangements of component partsdescribed in these embodiments are mere examples used only for thepurpose of explanation, and accordingly, are not intended to limit thetechnical scope of the present invention.

FIG. 1 is a longitudinal sectional view illustrating an essential partof a variable-throat exhaust turbocharger in a first embodiment of thepresent invention, and FIG. 2 is an enlarged view illustrating a Z partin FIG. 1, in the first embodiment.

Referring to FIGS. 1 and 2, there are shown a turbine casing 10, ascroll 11 formed in the outer peripheral part of the turbine casing, ina spiral shape, a radial flow turbine rotor 12 which is arranged,coaxial with a compressor 13 (refer to FIG. 12), the turbine rotor 12having a turbine shaft 12 a rotatably journalled to a bearing housing 13through the intermediary of bearings' 16, and a center axis 10 a of theexhaust turbocharger.

A plurality of nozzle vanes 2 are provided so as to be arranged in theinner peripheral side of the scroll 11, at equal intervals in thecircumferential direction of the turbine. Each of the nozzle vanes 2 iscoupled at its end part with a nozzle shaft 02 which is rotatablysupported on a nozzle mount 4 secured to the turbine casing 12, and isconfigured so as to change its blade angle by means of a variable nozzlemechanism 100.

In the variable nozzle mechanism 100, the nozzle vanes 2 are eacharranged between the nozzle mount 4 and an annular nozzle plate 6coupled to the nozzle mount 4 through the intermediary of a plurality ofnozzle supports 5. The nozzle plate 6 is fitted on an attaching part ofthe turbine casing 10.

Further, there are shown a drive ring 3 formed in a disc-like shape,which is rotatably supported in the turbine casing 10 and which arefixed thereto with drive pins 32 at equal intervals in thecircumferential direction, and lever plates 1 each having an input sidegroove which is engaged with the associated drive pin 32 and each havingan output side which is secured to the associated nozzle shaft.

Further, there are shown a link 15 coupled to an actuator (which is notshown) serving as a drive source for the nozzle vanes 2, and a pin 14coupled to the link 15. The pin 14 is engaged with the drive ring 3 soas to rotate the drive ring 3.

During the operation of the variable-throat exhaust turbo-chargerincorporating the variable nozzle mechanism having the above-mentionedconfiguration, exhaust gas from an engine (which is not shown) is ledinto the scroll 11 so as to be swirled along spiral passages in thescroll 11, then flowing into the nozzle vanes 2. The exhaust gas thenpasses through gaps between the nozzle vanes 2 and is led onto theturbine rotor 12 from the outer peripheral side of the latter.Thereafter, the exhaust gas radially flows toward the center axis of theturbine rotor so as to carry out expansive work for the turbine rotor12, and then axially flows out, being led into a gas outlet 10 b fromwhich it is discharged out from the turbocharger.

In order to control the delivery volume of the variable-throat exhaustturbocharger, the blade angle of the nozzle vanes 2 is set by an bladeangle control means (which is not shown) so as to regulate the flow rateof the exhaust gas flowing through the nozzle vanes 2 to a predeterminedvalue. The reciprocal displacement of the actuator in response to theblade angle is transmitted to the drive ring 3 through the intermediaryof the link 15 and the pin 14, and accordingly, the drive ring 3 isrotated.

The rotation of the drive ring 3 causes the drive pins 32 which aresecured to the drive ring 3 at equal intervals in the circumferentialdirection thereof, to rotate the lever plates 1 around the nozzle shafts02. The rotation of the nozzle shafts 02 turn the nozzle vanes 2 inorder to change the blade angle to a value set by the actuator.

The present invention concerns a mounting structure of the variablenozzle mechanism 100 in the variable-throat exhaust turbocharger havingthe above-mentioned configuration.

Embodiment 1

Referring to FIGS. 1 and 2, an insert member 20 which is annularlyformed is removably attached to the side surface of the bearing housing13 at the outer periphery of the nozzle mount 4 by means of a pluralityof fixing screws (screw caps) 21 which are circumferentially positioned.Thus, by fastening the insert member 20 to the bearing housing 13 whichcan be maintained at a low temperature, the value of heat transmissionfrom the turbine casing 10 at a high temperature can be reduced.Further, by providing the fixing screws 21 at positions in proximitywith the nozzle mount 4, the nozzle assembly can be prevented from beingdeformed or shifted as far as possible.

The turbine casing 10 is formed therein with an attaching bore 10 ahaving a diameter substantially equal to the outer diameter of thescroll 11, being extended from the scroll 11 to the baring housing 13.The outer peripheral part of the insert member 20 is fitted in theattaching bore 10 a at the inner periphery of the latter in a spigotconfiguration. The insert member 20 is axially positioned by a steppedpart 10 c. Further, the inert member 20 is also fixed to the turbinecasing 10, being clamped by the outer flange of the bearing housing 13which is also fastened to the turbine casing 10 by bolt screws 25.Further, the inner peripheral surface of the insert member 20 is fittedon the outer peripheral surface of the nozzle mount 4 in a spigotconfiguration, and is axially positioned by a stepped part 4 c.

Nail pins 22 serve as a detent for the nozzle mount 4. This nail pins 22are press-fitted in the bearing housing 13 through cutouts which areformed in the lever plates 1 at a plurality of circumferentialpositions, from the fitted part of the nozzle mount 4 in order to serveas a detent for the nozzle mount 4.

In the first embodiment as stated above, the nozzle assembly composed ofthe nozzle vanes 2, the nozzle shafts 02, the nozzle plates 6, thenozzle supports 5, the nozzle mount 4 and the like is fastened to thebearing housing 13 through the intermediary of the insert member 20.Thus, the nozzle assembly cannot be affected by a thermal deformation ofthe turbine casing, and an external force exerted to the turbine casing10. Accordingly, the nozzle assembly can be prevented from beingdeformed by these factors. Thereby it is possible to prevent the nozzleassembly from being deformed.

Thus, nozzle assembly can be firmly fixed to the turbine casing 10through the intermediary of the insert member 20 without decreasing thefastening force. Thus, it is possible to eliminate, as a probleminherent to the prior art, such a disadvantage that the nozzle assemblyis excited by vibration from the engine side so as to cause the nozzleassembly and the nozzle link mechanism coupled to the former to be worn,resulting in lowering of the function of the variable nozzle mechanism100, and as a result, the boost pressure (air supply pressure) fed intothe engine is greatly decreased.

Further, according to the present invention, the necessity of a flangefor stably fixing nozzle assembly is eliminated from the inner diameterside of the turbine casing 10, and accordingly, the insert member 20 canbe fitted in the part where the above-mentioned flange has beenprovided. Thus, the turbine casing itself may have such a configurationthat the outer peripheral part of the scroll is opened to the bearinghousing 13 in the axial direction, as the turbine casing is viewed as asingle component.

Thus, the configuration of mold cores during casting of the turbinecasing can be simplified, that is, the number of mold cores can bereduced, thereby it is possible to simplify the manufacture of theturbine casing 10. Further, since the turbine casing 10 is usuallycomposed of a casting, as stated above, the presence of burrs in thescroll 11 can be easily checked through the opened part as stated above.

Further, in the turbine casing 10 incorporating the scroll 11 in whichthe undercut part 11 s is formed, the outer peripheral part of thescroll 11 can be opened in the axial direction due to the provision ofthe insert member 20. Thus, even through the mold core is split, themanagement of the mold core can be facilitated, and accordingly, thenumber of mold cores can be greatly reduced in comparison with theconventional one.

Further, in the prior art, the scroll end (tongue-like part) isrestrained by the turbine casing 10 therewithin, and accordingly, athermal stress applied thereto becomes usually higher. On the contrary,in the first embodiment of the present invention, the scroll end issplit by the provision of the insert member 20 so as to relief therestraint, thereby it is possible to prevent the scroll end (tongue-likepart) from clacking.

Second Embodiment

FIG. 3 is a longitudinal sectional view illustrating an essential partof an upper half of a second embodiment of the present invention on theturbine side.

In this second embodiment, there is provided an integrated nozzle mounttype insert member 26 in which the nozzle mount 4 and the insert member20 that have been explained in the first embodiment are integrallyincorporated with each other. The above-mentioned integrated nozzlemount type insert member 26 is fitted at its outer periphery in anattaching bore 10 a which is formed in the turbine casing 10, beingopened from the scroll 11 toward the bearing housing 13. Further, theintegrated nozzle mount type insert member 26 is attached to the bearinghousing 13 by means of a plurality of fixing screws (cap screws) 21, asexplained in the first embodiment.

The above-mentioned integrated nozzle mount type insert member 26 isfixed to the turbine casing 10 being fastened together with the outerperipheral flange of the bearing housing by bolts 25 through theintermediary of a ring lock 27.

Except the above-mentioned configuration, the configuration of thesecond embodiment is the same as that of the first embodiment explainedwith reference to FIGS. 1 and 2, and accordingly, like referencenumerals are used to denote like parts to those explained in the firstembodiment.

In the second embodiment as stated above in which the nozzle mount 4 andthe insert member 20 are integrally incorporated with each other so asto form the integrated nozzle mount type insert member 26, it ispossible to more surely fasten the integrated nozzle mount type insertmember 26 to the bearing housing 13, in comparison with the firstembodiment. Thus, it is possible to aim at reducing the number ofcomponent parts in the second embodiment.

Further, since no seal surfaces are present at the outer diameter sideflange of the nozzle mount 4 and at the turbine inner diameter sideflange of the insert member 20, no risk of gas leakage would be caused.Accordingly, no severe dimensional management is required, thereby it ispossible to simplify the manufacture of the insert member 20.

Embodiment 3

FIG. 4 is a view which shows a third embodiment of the presentinvention, corresponding to FIG. 2.

In the third embodiment, the insert member 20 is formed in its outerperipheral part with a flange 20 s which is clamped between the flangeswhich are formed at the outer peripheries of the turbine casing 10 andthe bearing housing 13, and the thus clamped parts are joined at theirouter peripheries together in a fluid tight manner by means of acoupling 28. Except this configuration, the configuration of the thirdembodiment is the same as that of the first embodiment, and accordingly,like reference numerals are use to denote like parts to those explainedin the first embodiment.

In the third embodiment as stated above, since the insert member 20 canbe coupled by means of the single coupling 28 alone in a fluid tightmanner, the number of component parts can be reduced. Further, in thethird embodiment, three components, that is, the insert member 20, theturbine casing 10 and the bearing housing 13 are fastened at theiroutermost peripheral flanges by the coupling 28, and accordingly, thefastening can be made in a part which is held at a relatively lowertemperature. Thus, even though the coupling 28 is made of a relativelyinexpensive material, its fastening function can be satisfactory.

Embodiment 4

FIG. 5 is a view which illustrates a fourth embodiment of the presentinvention, corresponding to FIG. 2.

In the fourth embodiment, a snap ring 29 is fitted in a ring groove 30formed in the side end part of the turbine casing 10 on the bearinghousing 13 side. The outer peripheral parts of the bearing housing 13and the insert member 20 are clamped on the inside of the snap ring 29,that is, the bearing housing 13 and the insert member 20 are pressed andsecured against the turbine casing 10 by an inclined side surface 29 aof the snap ring 29. In this case, since the snap ring 29 has theinclined side surface 29 a, an axial force is generated by pushing thesnap ring 29 into the ring groove 30. By this axial force, the outerperipheral part of the insert member 20 can be firmly held between thebearing housing 13 and the turbine casing 10.

Except the above-mentioned configuration, the configuration of thefourth embodiment 1 is the same as that of the first embodiment shown inFIG. 1, and accordingly, like reference numerals are used to denote likeparts to those explained in the first embodiment.

In the fourth embodiment as stated above, with the provision of the snapring 29 for the fastened parts of the insert member 20, the turbinecasing 10 and the bearing housing 13, no risk of loosening of thefastening parts is caused, in comparison with the other embodimentsmentioned above, resulting in an increase in the fastening strengthagainst vibration transmitted from an engine. Further, with the use ofone single component, that is, the snap ring 29 alone, the fasteningmember can be provided, and accordingly, the number of component partscan be reduced.

Further, in the forth embodiment, the snap ring 29 is fitted in theinner diameter side of the attaching bore 10 in the turbine casing 10,thereby it is possible to avoid increasing the outer diametrical size ofthe fastened part of the insert member 20.

Fifth Embodiment

FIG. 6 is a view illustrating a fifth embodiment of the presentinvention, corresponding to FIG. 2.

In the fifth embodiment, a female thread is formed in the attaching bore10 b (refer to FIG. 1) in the turbine casing 10, and a male thread isformed at the outer peripheral part of the insert member 20. With theuse of the thread portion 30 s in which the female thread is meshed withthe male thread, the outer peripheral part of the insert member is fixedbetween the turbine casing 10 and the bearing housing 13.

Except the above-mentioned configuration, the configuration of the fifthembodiment is the same as that of the first embodiment. Thus, likereference numerals are used to denote like part to those explained inthe first embodiment.

In the fifth embodiment as stated above, the fastened parts of theinsert member 20 and the turbine casing 10 can be broadened. Thus, it ispossible to stably fasten the insert member 20.

Further, in the fifth embodiment, the insert member 20 can be readilyfastened to the turbine casing 10 by screwing the male thread of theformer into the female thread of the latter, no particular attachingscrew member is required, thereby it is possible to miniaturize theinsert member 20 itself.

Sixth Embodiment

FIG. 7 is a view for illustrating a sixth embodiment of the presentinvention, corresponding to FIG. 2.

In this sixth embodiment, the outer peripheral part of the insert member20 is fixed by welding to the outer peripheral parts of both bearinghousing 13 and the turbine casing 10, that is, by a welded part 33.

Except the above-mentioned matter, the configuration of this embodimentis the same as that of the first embodiment, and accordingly, likereference numerals are used to denote like parts to those explained inthe first embodiment.

In the sixth embodiment as stated above, no particular attaching screwmember and the like for fastening the insert member 20 to the bearinghousing 13 or the turbine casing 10 are required, thereby it is possibleto reduce the number of component parts. Further, in the sixthembodiment, since the fastening is made by welding 33, the welding canbe made around the sealing surfaces, thereby it is possible to minimizeoccurrence of gas leakage.

Seventh Embodiment

FIG. 8 is a view illustrating a seventh embodiment, corresponding toFIG. 2.

In the seventh embodiment, a piston ring 34 for fluid-tight sealing isfitted in a groove formed in the outer peripheral part of the insertmember 20, having an outer peripheral surface which is made intoslidable contact with the inner peripheral surface of the attaching bore10 b in the turbine casing 10. Alternatively, the piston ring 34 may befitted in a groove formed in the inner peripheral surface of theattaching bore 10 b in the turbine casing 10, having an inner peripheralsurface which is made into slidable contact with the outer peripheralsurface of the insert member 20.

Except the above-mentioned matter, the configuration of the seventhembodiment is the same as that of the first embodiment shown in FIG. 1,and accordingly, like reference numerals are used to denote like partsto those explained first embodiment.

In the seventh embodiment as stated above, gas leakage through thefitting portion between the insert member 20 and the turbine casing 10can be surely prevented by the piston ring 34 fitted in the fittingportion.

Eighth Embodiment

FIG. 9 is an eighth embodiment of the present invention, correspondingto FIG. 2.

In the eighth embodiment, a piston ring 35 is fitted in the grooveformed in the inner peripheral surface of the insert member 20, and hasan inner peripheral surface which is made into slidable contact with theouter peripheral surface of the nozzle mount 4. Alternatively, thepiston ring 35 may be fitted in a groove formed in the outer peripheralsurface of the nozzle mount 4, and has an outer peripheral surface whichis made into slidable contact with the inner peripheral surface of theinsert member 20.

Except the above-mentioned matter, the configuration of the eighthembodiment is the same as that of the first embodiment, and accordingly,like reference numerals are used to denote like parts to those explainedin the first embodiment.

In the above-mentioned eighth embodiment, gas leakage through thefitting portion between the inner periphery of the insert member 20 andthe outer periphery of the nozzle mount 4 can be surely prevented by thepiston ring 35. Further, the piston ring 35 does not exert anappreciably large force to its associated component, thereby it ispossible to avoid causing a risk of deformation of the nozzle mount 4due to the fitting of the piston ring 35, and so forth.

Ninth Embodiment

FIG. 10 is a longitudinal sectional view illustrating an essential partof a turbine casing in a ninth embodiment of the present invention.

In this ninth embodiment, the scroll 11 in the turbine casing 10 isformed therein with an opening which is axially straight forward so asto have no protrusion projected from the inner peripheral part to theouter peripheral part of the scroll 11. Further, the opening is attachedthereto with an insert shroud 36 having a protrusion 36 y projectedtoward the outer periphery of the scroll 11 and serving as a part of theinner peripheral surface of the scroll 11, and the insert shroud 36 isformed therein with an annular nozzle plate 36 z adapted to be coupledto the nozzle mount 4 through the intermediary of the nozzle supports 5.The insert shroud 36 is positioned in the turbine casing 10 at an innerspigot part 36 a.

Further, the insert shroud 36 is located on the inside of the nozzleplates 6, and is fixed to the opening end surface of the turbine casing10 by means of screw caps 27 provided along the inner periphery.

In the prior art, the scroll of the turbine casing 10 made by casting isformed only by casting, and accordingly, should an undercut 11 s beformed in the scroll 11 as shown in FIG. 12, a mold core for the scrollshould have a split structure. On the contrary, in the ninth embodimentas stated above, the scroll 11 is spirit in part, and is formed thereinwith the opening which is axially straightforward, having no protrusionprojected from the inner periphery toward the outer periphery of thescroll 11. Further, the opening is provided therein with an insertshroud 36 having the protrusion 36 y projected toward the outerperipheral surface of the scroll and serving as a part of the innersurface of the scroll 11. Thus, the scroll 11 is axially opened.

With this configuration, the undercut part 11 s as in the prior art isformed by the insert shroud 36, thereby it is possible to manufacturethe turbine casing 10 from an inexpensive casting having such aconfiguration as to sustain satisfactory aerodynamic performance and toprevent the mold core for the scroll 11 from being formed in a splitstructure.

Further, although the insert shroud 36 is fastened to the turbine casing10 by the plurality of screw caps 37, the drilling for the fastening ismade in a direction the same as those of the other bolt holes and thelike in the turbine casing 10. Thus, no planning for changing thedirection of the drilling is required, thereby it is possible tominimize an increase in the working man-hours for the drilling.

Further, the fastened part of the insert shroud 36 is faced to theinside of the nozzle plate 6, and accordingly, the screw caps 37 are notexposed to the gas passage, thereby it is possible to prevent the screwcaps 37 from being directly made into contact with the exhaust gas.Thus, the screw caps 37 themselves can be made of inexpensive materials.Further, even though the screw caps are loosened, their fastenedcondition can be maintained since the screw caps 37 are retained by thenozzle plate 6 which is arranged adjacent thereto.

It is noted that the insert shroud 36 may be fixed to the turbine casing10, direct thereto by shrinkage fitting with no use of the plurality ofcap screws 37. With this configuration, the spigot parts in both insertshroud 36 and the turbine casing 10 may be made to be longer, thereby itis possible to ensure stable fastening.

Tenth Embodiment

FIG. 11 is a view illustrating a tenth embodiment of the presentinvention, corresponding to FIG. 1.

The tenth embodiment is has a configuration which is in combination ofthose of the first embodiment shown in FIGS. 1 and 2, and the ninthembodiment shown in FIG. 10. That is, the above-mentioned insert member20 which are annularly formed is removably attached to the outerperiphery of the nozzle mount 4 by means of a plurality of fixing screws21. Further, in the tenth embodiment, the insert member 20 is fitted atits outer periphery in the attaching bore 10 a which is formed in theturbine casing 10, being opened from the scroll 11 toward the bearinghousing 13. The configuration of the first embodiment in which theinsert member 20 is attached to the bearing housing 13, is combined withthe configuration of the ninth embodiment in which the axially linearopening having no protrusion that is projected from the inner peripheralsurface toward the outer peripheral surface of the scroll 11 is formed,and in which the insert shroud 36 having the protrusion 36 y projectedtoward the outer periphery and serving as a part of the inner surface ofthe scroll 11 is attached to the opening while a support part 36 z forthe annular nozzle plate 6 that is coupled to the nozzle mount 4 throughthe intermediary of the nozzle supports 4 is formed in the insert shroud36.

In the tenth embodiment as stated above, the technical effects andadvantages which are synergistic in combination of the first and ninthembodiments can be obtained, and as a result, the structure for mountingthe variable nozzle structure which is practically excellent can beobtained in the variable-throat exhaust turbo-supercharge.

According to the present invention, there can be provided a nozzleassembly including a nozzle mount and nozzle vanes, which has a firmsupport structure without being affected by a thermal deformation of theturbine casing and an external force exerted to the turbine casing.Further, according to the present invention, the configuration of thescroll is simplified so as to be substantially opened, and accordingly,the nozzle assembly can be simply formed. Further, according to thepresent invention, there can be provided a variable-throat exhaustturbocharger which is manufactured with a reduced number of mold coresfor the scroll, that are used during casting of the turbine casing,thereby it is possible to enhance the productivity of the turbinecasing.

According to the present invention, the annularly formed insert memberis removable attached to the outer periphery of the nozzle mount.Further, according to the present invention, the insert member is fittedat its outer periphery in the attaching bore formed in the turbinecasing and opened from the scroll toward the bearing housing so as toattach the insert member to the bearing housing, thereby it is possibleto obtain the following technical effects and advantages:

(1) According to the present invention, by fastening the nozzle assemblyto the bearing housing side through the intermediary of the insertmember, the nozzle assembly can be prevented from being affected by athermal deformation of the turbine casing and an external force exertedto the turbine casing, and accordingly, it is possible to prevent thenozzle assembly from being deformed thereby. With this configuration,the nozzle assembly can be firmly secured to the turbine casing sidewithout decreasing the fastening force. Thus, there can be preventedoccurrence of such a disadvantage, or a problem inherent to the priorart, that the nozzle assembly is excited by vibration from the engineside, resulting in abrasion of the nozzle assembly and the nozzle linkmechanism coupled to the former, and accordingly, the function of thevariable nozzle mechanism is deteriorated so that the boost pressure(air supply pressure) into the engine is largely lowered;(2) According to the present invention, the necessity of a flange, onthe inner diameter side of the turbine casing, with which the nozzleassembly can be stably fixed, can be eliminated, and accordingly, theinsert member can be fitted in the part where the flange has beenconventionally formed. Thus, there may be provided such a configurationthat the scroll is axially opened toward the bearing casing in its outerperipheral part, as the turbine casing itself is viewed as a singlecomponent. Thus the configuration of mold cores used during casting ofthe turbine casing can be simplified, and accordingly, the number of themold cores can be reduced. Thus, the manufacture of the turbine casingcan be simplified. Further, since the turbine casing is usually formedfrom castings, it is possible to check the presence of burrs in thescroll through the opening part of the bearing housing.(3) According to the present invention, in the turbine casingincorporating the scroll with the undercut, the outer peripheral part ofthe scroll can be axially opened by providing the insert member. Thus,even though the mold cores are split, the management of the mold corescan be simplified, and accordingly, the number of mold cores can begreatly reduced in comparison with the prior art.(4) Since the scroll end (tongue part) in the prior art has beenrestrained in the turbine casing, a higher thermal stress has beennormally caused. On the contrary, according to the present invention,the scroll end is split by the insert member so as to reduce therestraint, thereby it is possible to prevent the scroll end (tonguepart) from cracking.

Further, in the present invention, the nozzle mount and the insertmember are integrally incorporated with each other so as to constitutethe integrated nozzle mount type insert member. The integrated nozzlemount type insert member is fitted at its outer periphery in theattaching bore which is formed in the turbine casing, being opened fromthe scroll toward the bearing housing. The integrated nozzle mount typeinsert member is attached to the bearing housing by fastening meansincluding attaching screws. With this configuration, the integratednozzle mount type insert member can be more surely fastened to thebearing housing. Further, the number of component parts can be reduced.

Further, since no seal surfaces are present at the flange of the nozzlemount on the inner diameter side and the flange of the insert member onthe turbine inner diameter side as stated above, no risk of gas leakagewould be caused. Thus, no severe dimensional management is required,thereby it is possible to simplify the manufacture of the insert member.

Further, in the present invention, the flange part is formed in theouter peripheral part of the insert member. This flange part is clampedbetween the flange parts formed in the turbine casing and the bearinghousing. Further, the thus obtained clamped parts are joined by thecoupling in the fluid tight manner. With this configuration, the insertmember is coupled in a fluid tight manner with the use of only a singlecoupling, thereby it is possible to reduce the number of componentparts.

Further, the above-mentioned three components, that is, the insertmember, the turbine casing and the bearing housing, are fastened attheir outer peripheral flange parts by the coupling, and accordingly,they can be fastened in a part where the temperature is held at arelatively low value. The coupling which is even made of relativelyinexpensive materials can satisfy its fastening function.

Further, in the present invention, the snap ring is fitted in the ringgroove formed in the bearing side end part of the turbine casing. Theouter peripheral parts of the bearing housing and the insert member areclamped on the inside of the snap ring, and accordingly, the bearinghousing and the insert member are fixed against the turbine casing by aside surface of the snap ring. With this configuration in which the snapring is used in the fastened parts of the insert member, the turbinecasing and the bearing housing, no risk of loosening of the fastenedpart would be caused, in comparison with the above-mentionedembodiments, thereby it is possible to enhance the fastening strengthagainst vibration from the engine.

Further, according to the present invention, the fastening member can beconstituted only by the single snap ring itself, and accordingly, thenumber of component parts can be reduced. Further, since the snap ringis fitted in the inner diameter side of the turbine casing, thereby itis possible to avoid increasing the outer diameter size of the fastenedparts.

Further, in the present invention, the female thread is formed in theattaching bore in the turbine casing, and the male thread is formed atthe outer periphery of the insert member. By meshing the female threadwith the male thread, the outer peripheral part of the insert member isfixed between the turbine casing and the bearing housing. With thisconfiguration, the part where the insert member and the turbine casingare fastened can be broadened. Thus, the insert member can be stablyfastened. Further, since only the insert member itself can be fastenedto the turbine casing, any particular attaching screw is not required.Thus, the insert member itself can be miniaturized.

Further, in the present invention, the outer peripheral part of theinsert member is fixed to the bearing housing and the turbine casing bywelding. Thus, no any particular attaching screw for fastening theinsert member to the bearing housing or the turbine casing is required.Thereby it is possible to reduce the number of component parts.

Further, since the fastening is made by welding, the part around theseal surface can be welded, thereby it is possible to minimize gasleakage.

Further, in the present invention, the piston ring for fluid-tightsealing is fitted between the outer periphery of the insert member andthe inner periphery of the attaching bore in the turbine casing. Theouter peripheral surface of the piston ring is made into slidablecontact with the inner peripheral surface of the attaching bore in theturbine casing. With this configuration, gas leakage from the fastenedpart between the insert member and the turbine casing can be preventedby the piston ring fitted in the fastened part.

Further, in the present invention, the piston ring for fluid tightsealing is fitted between the inner peripheral surface of the insertmember and the outer peripheral surface of the nozzle mount faced to theformer. With this configuration, gas leakage from the fitted partbetween the insert member and the turbine casing can be prevented by thepiston ring. Further, since the piston ring does not exert a force whichis relatively large, to its associated part, it is not required to takecare of a risk of deformation of the nozzle mount due to the fitting ofthe piston ring.

Further, in the prior art, the scroll of the turbine casing formed bycasting has been formed of a casting alone. Thus, should the undercutpart 11 s be formed in the scroll as shown in FIG. 12, a mold core forthe scroll should have a split structure.

On the contrary, according to the present invention, the opening whichhas no protrusion projected from the inner periphery toward the outerperiphery of the scroll and which is axially linear is formed in theturbine casing. Further, the insert shroud having a protrusion projectedtoward the outer periphery of the scroll and serving as a part of theinner surface of the scroll is attached to the opening, and the supportpart of the annular nozzle plate which is coupled to the nozzle mountthrough the intermediary of the nozzle supports are formed in the insertshroud. Thus, the scroll has a partially split structure, and theopening having no protrusion projected from the inner peripheral parttoward the outer peripheral part of the scroll and which is axiallylinear is formed in the scroll. Further, the insert shroud having theprotrusion projected toward the outer periphery and serving as a part ofthe inner surface of the scroll is attached to the opening, andaccordingly, the scroll can be axially opened.

With this configuration, the undercut part as in the prior art is formedby the insert shroud, thereby it is possible to manufacture the turbinecasing in an inexpensive casting configuration without using a splittype mold core for the scroll while a satisfactory aerodynamicperformance can be maintained.

Further, in the present invention, the insert shroud is fastened to theturbine casing with the use of a plurality of screw members (cap screwsor the like), and drilling for the fastening is in a direction which isthe same as that of other bolts holes or the like in the turbine casing,thereby it is possible to eliminate the necessity of such a planningthat the direction of the drilling is changed. Thus, it is possible tominimize an increase in the man hours for the drilling.

Further, since the fastened part of the insert shroud is faced to thenozzle plates, the screw members (cap screws) are prevented from beingexposed to the gas passage, thereby it is possible to prevent the screwmembers from being exposed to the exhaust gas. Accordingly, the screwmembers (cap screws) themselves can be made of inexpensive materials.Further, even though the screw members are loosened, the screw memberscan be retained by the nozzle plate which is arranged, adjacent thereto,the fastening thereof can be maintained.

It is noted that the insert shroud may be directly fixed to the turbinecasing by means of shrinkage fitting or the like without using aplurality of screw members (cap screws) as stated above. With thisconfiguration, the spigot parts of both insert shroud and the turbinecasing are made to be longer, thereby it is possible to obtain stablefastening.

Further, the present invention can include a configuration incombination of claim 1 and claim 10. With this configuration, synergetictechnical effects and advantages can be obtained from the configurationstated in claim 1 and that stated in claim 10, thereby it is possible toobtain an attaching structure of the variable nozzle mechanism which ispractically excellent, in a variable-throat exhaust turbocharger.

1. A mounting structure for a variable nozzle mechanism which isincorporated in a variable-throat exhaust turbocharger, and in whichexhaust gas from an engine is led through a scroll formed in a turbinecasing, and a plurality of nozzle vanes arranged on the inner peripheralside of the scroll, and is then applied to a turbine rotor provided inthe inner peripheral side of the nozzle vanes, and the plurality ofnozzle vanes are rotatably supported on an annular nozzle mount so as tochange the blade angle of the nozzle vanes in order to regulate the flowrate of the exhaust gas applied onto the turbine rotor, characterized inthat an annularly formed insert member is removable attached to theouter periphery of the nozzle mount, and the insert member is fitted atits outer periphery in an attaching bore which is formed in the turbinecasing and which is opened from the scroll toward a bearing housing, andthe insert member is attached to the bearing housing.
 2. A mountingstructure for a variable nozzle mechanism which is incorporated in avariable-throat exhaust turbocharger, and in which exhaust gas from anengine is led through a scroll formed in a turbine casing, and aplurality of nozzle vanes arranged on the inner peripheral side of thescroll, and is then applied to a turbine rotor provided in the innerperipheral side of the nozzle vanes, and the plurality of nozzle vanesare rotatably supported on an annular nozzle mount so as to change theblade angle of the nozzle vanes in order to regulate the flow rate ofthe exhaust gas applied onto the turbine rotor, characterized in thatthe nozzle mount and an insert member are integrally incorporated witheach other so as to form an integrated nozzle mount type insert member,the integrated nozzle mount type insert member is fitted at its outerperiphery in an attaching bore which is formed in the turbine casing andwhich is opened from the scroll toward a bearing housing, and theintegrated nozzle mount type insert member is attached to the bearinghousing.
 3. A mounting structure for a variable nozzle mechanism in avariable-throat exhaust turbocharger according to claim 2, characterizedin that the insert member is attached thereto with the nozzle mount anda variable nozzle mechanism member including the nozzle vanes attachedto the nozzle mount so as to form an integrated nozzle mount and insertmember assembly structure, and the nozzle mount and insert memberassembly structure is fixed to the bearing housing by fastening membersincluding bolts and attaching screws.
 4. A mounting structure for avariable nozzle mechanism in a variable-throat exhaust turbochargeraccording to claim 1, characterized in that the inset member is formedin its outer peripheral part with a flange part, the flange part isclamped between flange parts formed in the turbine casing and thebearing housing, and the thus formed clamped parts are joined at theirouter peripheries by a coupling in a fluid tight manner.
 5. A mountingstructure for a variable nozzle mechanism in a variable-throat exhaustturbocharger according to claim 1, characterized in that a snap ring isfitted in a ring groove formed in a side end part of the bearing housingin the turbine casing, and the outer peripheral parts of the bearinghousing and the insert member are clamped between the snap ring and theturbine casing, and the bearing housing and the insert member are fixedto the turbine casing by a side surface of the snap ring.
 6. A mountingstructure for a variable nozzle mechanism in a variable-throat exhaustturbocharger according to claim 1, characterized in that a female threadis formed in the attaching bore in the turbine casing while a malethread is formed at the outer periphery of the insert member, and theouter peripheral part of the insert member is fixed between the turbinecasing and the bearing housing by meshing the female thread with themale thread.
 7. A mounting structure for a variable nozzle mechanism ina variable-throat exhaust turbocharger according to claim 1,characterized in that the outer peripheral part of the insert member isfixed to the bearing housing and the turbine casing by welding.
 8. Amounting structure for a variable nozzle mechanism in a variable-throatexhaust turbocharger according to claim 1, characterized in that apiston ring for fluid tight sealing is fitted between the outerperiphery of the insert member and the inner periphery of the attachingbore in the turbine casing, and the outer peripheral surface of thepiston ring is made into slidable contact with the inner peripheralsurface of the attaching bore in the turbine casing.
 9. A mountingstructure for a variable nozzle mechanism in a variable-throat exhaustturbocharger according to claim 1, characterized in that a piston ringfor fluid tight sealing is fitted between the inner peripheral surfaceof the insert member and the outer peripheral surface of the nozzlemount which is faced to the inner peripheral surface.
 10. A mountingstructure for a variable nozzle mechanism which is incorporated in avariable-throat exhaust turbocharger, and in which exhaust gas from anengine is led through a scroll formed in a turbine casing, and aplurality of nozzle vanes arranged on the inner peripheral side of thescroll, and is then applied to a turbine rotor provided in the innerperipheral side of the nozzle vanes, and the plurality of nozzle vanesare rotatably supported on an annular nozzle mount so as to change theblade angle of the nozzle vanes in order to regulate the flow rate ofthe exhaust gas applied onto the turbine rotor, characterized in thatthe turbine casing is formed therein with an opening which has noprotrusion projected from the inner peripheral surface toward the outerperiphery surface of the scroll, and which is axially linear, an insertshroud having a protrusion which is projected toward the outer peripheryof the scroll and which serves as a part of the inner surface of thescroll is attached to the opening, and a support part of an annularnozzle plate which is coupled to the nozzle mount through theintermediary of a nozzle support is formed in the insert shroud.
 11. Amounting structure for a variable nozzle mechanism which is incorporatedin a variable-throat exhaust turbocharger, and in which exhaust gas froman engine is led through a scroll formed in a turbine casing, and aplurality of nozzle vanes arranged on the inner peripheral side of thescroll, and is then applied to a turbine rotor provided in the innerperipheral side of the nozzle vanes, and the plurality of nozzle vanesare rotatably supported on an annular nozzle mount so as to change theblade angle of the nozzle vanes in order to regulate the flow rate ofthe exhaust gas applied onto the turbine rotor, characterized in that anannularly formed insert member is removable attached to the outerperiphery of the nozzle mount, and the insert member is fitted at itsouter periphery in an attaching bore which is formed in the turbinecasing and which is opened from the scroll toward the bearing housing,the insert member is attached to the bearing housing, further, theturbine casing is formed therein with an opening which has no protrusionprojected from the inner peripheral surface toward the outer peripheralsurface of the scroll and which is axially linear, an insert shroudhaving a protrusion which is projected toward the outer periphery of thescroll and which serves as a part of the inner surface of the scroll isattached to the opening, and a support part of an annular nozzle platecoupled to the nozzle mount through the intermediary of a nozzle supportis formed in the insert shroud.
 12. A mounting structure for a variablenozzle mechanism in a variable-throat exhaust turbocharger according toclaim 2, characterized in that the inset member is formed in its outerperipheral part with a flange part, the flange part is clamped betweenflange parts formed in the turbine casing and the bearing housing, andthe thus formed clamped parts are joined at their outer peripheries by acoupling in a fluid tight manner.
 13. A mounting structure for avariable nozzle mechanism in a variable-throat exhaust turbochargeraccording to claim 2, characterized in that a snap ring is fitted in aring groove formed in a side end part of the bearing housing in theturbine casing, and the outer peripheral parts of the bearing housingand the insert member are clamped between the snap ring and the turbinecasing, and the bearing housing and the insert member are fixed to theturbine casing by a side surface of the snap ring.
 14. A mountingstructure for a variable nozzle mechanism in a variable-throat exhaustturbocharger according to claim 2, characterized in that a female threadis formed in the attaching bore in the turbine casing while a malethread is formed at the outer periphery of the insert member, and theouter peripheral part of the insert member is fixed between the turbinecasing and the bearing housing by meshing the female thread with themale thread.
 15. A mounting structure for a variable nozzle mechanism ina variable-throat exhaust turbocharger according to claim 2,characterized in that the outer peripheral part of the insert member isfixed to the bearing housing and the turbine casing by welding.
 16. Amounting structure for a variable nozzle mechanism in a variable-throatexhaust turbocharger according to claim 2, characterized in that apiston ring for fluid tight sealing is fitted between the outerperiphery of the insert member and the inner periphery of the attachingbore in the turbine casing, and the outer peripheral surface of thepiston ring is made into slidable contact with the inner peripheralsurface of the attaching bore in the turbine casing.